1. Field of the Invention
The present invention relates to a light guide, especially to a stepped light guide to diffuse light generated from a side light source to produce even lighting.
2. Description of the Related Art
A conventional light guide is utilized with linear light sources or at least one point light source to diffuse emitted light as a uniform surface light source. A conventional light guide may be rectangular-shaped or wedge-shaped and has an incident surface, an emitting surface and a reflective surface. The incident surface allows photons from a light source to enter. The emitting surface is adjacent to the incident surface transmits photons out of the light guide. The reflective surface is opposite to the emitting surface and adjacent to the incident surface and has a geometric structure. The geometric structure guides photons from the incident surface toward the emitting surface. Various patents, including U.S. Pat. No. 5,341,231, U.S. Pat. No. 6,328,453, U.S. Pat. No. 6,729,737, U.S. Pat. No. 6,752,507, Taiwan Patent No. 452088 and Taiwan Patent No. 428765, are related to changes in surface composition or geometric structure, and may comprise multiple reflectors implemented as V-cut grooves, annular protrusions, dots or the like.
However, light intensity over the emitting surface is inconsistent, a problem related to mainly patents, including, U.S. Pat. No. 6,099,134 disclosing a back lighting unit including a light guide provided with a random dot disposition pattern so that luminance of the backlighting unit is uniform over the surface thereof.
In U.S. Pat. No. 5,093,765, one major surface of a light guide is partially covered with a light diffusing material under specified conditions having a higher refractive index than the light guide.
As outlined above, conventional light guides produce a consistent light intensity by using complicated microstructures, such as dot patterns, protrusions or grooves to guide photons toward the emitting surface. The conventional light guide may be further combined with optical films, like reflectors, a diffuser or a prism sheet to improve illumination of the surface light source.
It is desired to provide a light guide that has a simple structure and can effectively diffuse light generated from a side light source to produce even lighting without depending on other optical films.